Should You Budget Fungicides for Managing FHB?

To spray or not to spray is a common question among grain growers in areas where scab has been a threat

By Don Lilliboe

Higher prices and the ability to accurately predict moisture and temperature patterns would remove much stress from the life of the average wheat grower. But let’s deal with reality: Prices are what they are, and no sane meteorologist would consider tacking an iron-clad guarantee onto his or her long-term weather forecast.

That brings us to the topic at hand: whether to apply a fungicide to your wheat fields for the suppression of Fusarium Head Blight (FHB, commonly known as scab). In these tough economic times, when growers must closely weigh every input’s cost vs. return, applying a scab fungicide is seldom an automatic decision.

But should it be? As with so many management decisions, this one depends on variables: where you farm; which crop you’re talking about (spring wheat, durum, barley); history of the disease in your vicinity; whether you’re in a reduced-tillage system; infection predictions; and, of course, rainfall patterns and predictions.

Greg Daws is one spring wheat producer who routinely plugs fungicides into his operating budget. Daws, who farms near Michigan, N.D., typically treats his wheat twice with fungicide:  1) a reduced-rate early season application of Stratego or Tilt for control of leaf diseases like rust, tan spot and Septoria, and 2) an at-heading full-label-rate application of Folicur for suppression of scab. Daws and father Richard have been leaving check strips for two decades, and report yield benefits ranging from two bushels per acre all the way up to 20.  

Look at Disease, Crop Potential
Jochum Wiersma, small grains specialist with the University of Minnesota’s Northwest Research & Outlook Center at Crookston, has been on the front lines of the Fusarium Head Blight issue for several years. In determining whether to apply a fungicide, the basic premise has been to “look at the disease picture and the potential of the crop,” he says.

Previous research had indicated that the use of a foliar fungicide like Tilt at flag leaf emergence was economically viable if weather conditions were favorable for the leaf diseases and the yield potential looked good. “With changes in labeling that allowed for the use of Tilt or Folicur at the beginning of anthesis, the management decision became one of whether delaying a single application from flag leaf emergence to anthesis could be profitable,” he explains.

To answer that question, researchers, extension educators and farmers have, in recent years, kept a close eye on 1) weather conditions during the weeks prior to anthesis and  2) the development of any of the leaf diseases. With the help of a disease forecasting system (see more following this article) and more intensive scouting, many individuals became very comfortable with the decision to spray a fungicide at anthesis—if weather conditions had been favorable for disease development.

“The ‘01 growing season proved frustrating, in that we ended up with some significant levels of leaf diseases and FHB despite a very hot and dry June and first two weeks of July,” Wiersma notes. “A large portion of the spring wheat crop reached anthesis during the first week of July—a time when weather conditions were very counter-indicative of any disease development.”

Wiersma says the available fungicide products need to be applied no later than anthesis to maximize their level of protection and increase the chances of an economic return. “Based on the conditions at that time, the application of a fungicide to control leaf diseases and suppress FHB did not seem to make much sense,” Wiersma notes.

However, within a week after the critical decision time, weather conditions changed drastically and ample rainfall allowed leaf diseases and FHB to flourish. “In hindsight, it appears a fungicide application at anthesis might have resulted in an economic return, despite the lack of precipitation and conditions favorable for disease development in the critical two to three weeks prior to anthesis,” Wiersma says.

For Marcia McMullen, the question of whether to spray for FHB cannot be answered with a blanket recommendation. The North Dakota State University extension plant pathologist agrees that experience to-date suggests most spring wheat producers in the northwestern Minnesota/northeastern North Dakota area should benefit from a fungicide treatment. That’s not necessarily the case further west in North Dakota, however. In north central and northwest North Dakota, McMullen believes the decision to use fungicides may be more difficult, because of the long-term history of having lower rainfall and fewer days with high humidities.  However, in the last two years, high humidities and frequent rainfalls did coincide with flowering of the wheat and durum crops in these areas, and FHB levels were frequently severe.

“Durum producers in the region who did use fungicides for scab suppression last year were generally not very happy with the results,” McMullen says. She speculates that it could be a timing issue, a delivery-to-target problem; and/or “it may be that the environment was so overwhelmingly favorable in some of those regions for two or three weeks” that the fungicide simply couldn’t effectively suppress the disease.

Compared to producer experiences, last year’s NDSU fungicide trials in northwestern North Dakota resulted in good suppression of FHB in durum.  “But we never get quite as good results with durum as with spring wheat,” McMullen notes. “I think it’s the ‘nature of the beast.’ Durum is more susceptible genetically and sources of resistance for durum have been more difficult to find and incorporate into acceptable varieties. We also have a little harder time getting the fungicide into the site of infection, because the awns on durum are so long and the surface of the grain heads appear to repel water. We’ve also not been as successful with barley,” she adds.  “We can reduce the FHB severity by 50% or more, but we’ve generally been unsuccessful in reducing the DON content (vomitoxin) down to the levels required by the malting industry.”

Cost Vs. Benefit
Though the percentage of Northern Plains wheat and barley producers using fungicides has increased significantly during the past five years, Wiersma knows there’s still considerable grower (and lender) hesitance due to already squeezed operating budgets. His position, however, is that the region’s small grain farmers should strive to be lowest-cost producers on a per-bushel basis, not on a per-acre basis. And an effective fungicide treatment can help them achieve that objective, he believes.

“When I look at an input — whether it’s a herbicide, fungicide, (or other product) — I view it not on a per-acre basis, (but in terms of) likely investment,” Wiersma says. “If it appears to promise even a slight dividend, the product will go on, because it lowers my cost of production per bushel.”

Taking that step is not easy, Wiersma concedes. Treating 1,000 acres at $15 an acre (product + application) represents another $15,000 outlay toward the end of an already budget-stretching growing season. “It takes extremely strong nerves to say ‘I’m going to put another $15,000 into the crop’ that late in the season,” he says.

University analyses suggest, however, that fungicide applications usually payoff — at least in spring wheat. “Fungicides do not hurt the crop,” Wiersma observes, “and in 80% of cases, I believe we have a break-even (result) or better.”

He points to data from 1998 showing that the average reduction in FHB severity in treated hard red spring wheat in the tri-state region (Minnesota, North Dakota, South Dakota) ranged between 31 and 54%, depending on which fungicide was used. Simultaneously, HRSW yields that year increased by 25.1 to 48.5% (again, depending on the fungicide used). The amount of DON likewise was reduced, resulting in more-marketable crops.

NDSU’s McMullen notes that over the past several years, the average yield response in eastern North Dakota commercial spring wheat fields treated with a FHB-suppressing fungicide has been about 20%.

Application Method, Timing Critical
Maximizing a fungicide’s efficacy in FHB suppression requires optimum timing of application. The two most popular products — Folicur and Tilt — are broad-spectrum fungicides from the same class of chemistry. Both suppress FHB, though Folicur appears to hold an edge.  Folicur can provide up to a 50-60% reduction in FHB, accompanied by a similar level of reduction in the percentage of damaged kernels.

These products act mainly as pro-tectants. They do have some local systemic activity, meaning they’ll “seep” into those plant sites with which they make contact; but they do not translocate throughout the plant. So they must be delivered to the location where they are needed. In the case of FHB in small grains, it’s the plant head.  Application delivery is important to treatment efficacy, and Wiersma prefers a ground application versus air. “I like the flexibility (offered by ground spraying) and the fact that you can do 15 gallons of water per acre and get that coverage, which is so important.” 

Wiersma says another critical aspect is timing, which is often complicated by the desire to treat for leaf diseases at the same time as FHB. While leaf diseases in spring wheat used to be managed primarily via resistant varieties, the introduction of lines which are more tolerant to FHB concurrently has increased sensitivity to the leaf diseases.

Work done by U of M and NDSU plant pathologists has provided some quite clear-cut economics of spraying for leaf diseases, according to Wiersma. The trick comes in trying to control both the leaf diseases and FHB with a single fungicide application. Applying at the flag leaf stage is best for leaf disease control; but waiting until heading is required for effective FHB suppression. “The question becomes whether we can delay that treatment to heading, knowing we’re going to have suppression of scab and the benefits of leaf disease control,” Wiersma says.

Marcia McMullen says the answer to that question is yes. “We’ve had excellent success in also controlling leaf diseases with our scab treatments,” she notes.

 Playing the Odds
McMullen agrees with Wiersma that spring wheat growers in parts of the Red River Valley with a history of serious FHB should be budgeting for at least one fungicide application. For growers further west, however, “it’s a tougher call,” she states. Those growers need to take a variety of factors into consideration. For instance:

Are they in a reduced- or no-till production system? If so, that means more residue on the soil surface, which translates into additional host material for Fusarium inoculum.

Are sunflower, canola, soybeans or other non-host crops interspersed in the rotation? The risk of FHB increases when small grains are planted in FHB-infected grain residue from the previous crop year (or on old corn ground, since species of Fusarium which cause FHB can survive in corn residue for several years).

Are the spring wheat varieties you grow tolerant to FHB? Though there presently are no completely resistant varieties, some cultivars (such as Gunner and Alsen) do possess significantly more tolerance to FHB than others and will yield better under moderate infection levels.

Planting date also can affect FHB incidence. McMullen did not, for instance, recommend a scab fungicide treatment last year for many southeastern North Dakota wheat fields. Why not? Because by the time regular rains began falling in the Fargo area (mid-July), “most of the spring wheat crop in (the southern Red River Valley) had already flowered and was well into grain fill.” Simultaneously, many northern Red River Valley fields benefited from a fungicide since they weren’t as far along when the wet period began.  “The crop is most susceptible from early flowering up through early grain fill,” McMullen points out. “If you have extended wet weather during that period, it will be very favorable for this disease.”

Marcia McMullen, NDSU extension plant pathologist, said that the average severity of fusarium head blight or scab in North Dakota last year was generally low, although there were hot spots where FHB was severe, mostly in the north central part of the state. “The number of hours of humidity greater than 90% really contributed to the formation of this disease,” said McMullen. “This fungus likes 10 hours or more of continuous high humidity, and coinciding with grain flowering, this can cause scab infection.” The proper use of fungicides on wheat at early flowering have proven economically beneficial in areas where scab has been a problem. She advises producers budget and plan on using fungicides if wheat is planted where scab has been a problem.  “And if weather conditions are such that it doesn’t become a problem, then don’t spray,” she says.